It may not be related to the Antec Nine Hundred case but possibly other computer components such as the Power Supply. It would help if you can listen to where the sound is and then figure which one is causing the issue. If it's possibly the Nine Hundred case fan causing the noise we might be able to assist you in a getting a replacement. Please visit http://www.antec.com/support/
and fill in a trouble ticket.
Antec Support Team